W5500 with reference RJ45 magjack design: link-up issue on custom 2-layer board

shiohamu_d · 2026-05-02T22:18:50+09:00

Hello, I am having trouble with the PHY side of a W5500 design and would like to ask for advice on the PCB/layout around the RJ45 magjack. Summary Device: W5500 in LQFP-48 Interface to MCU: SPI MCU: ESP32-Dev Board: 2-layer PCB, top-side component placement RJ45: ARJM11A1-009-AB-EW2 magjack Design basis: W5500-Ref-RJ45With reference schematic Power supply: LM2576S-3.3 SPI communication is working correctly. I can read the version register. When I replace the W5500 section with a module, the device can ping 192.168.1.7/24 successfully, so I believe the SPI side is fine. Symptoms With mode = 000 and 011, the link comes up. However, the router never shows proper communication/ACKs. With mode = 001, 010, or 100, the link does not come up at all. In mode = 000, I also see about 7 blinks on the relevant LED/activity indication. Wiring / layout details TXP → pin 1 TXN → pin 2 RXP → pin 3 RXN → pin 6 RX side uses capacitors, as in the reference design Differential pairs are routed with GND beneath them The area under the RJ45 is kept free of copper Only the RJ45 shield / CGND pin (pin 8) is connected to the CGND side GND and CGND are separated using a 1 nF, 1 kV capacitor I used BLM18PG121SN1D instead of HH-1M1608-121JT Decoupling capacitors are the same as the reference circuit RESETn is controlled by the ESP32-Dev The reset timing is not measured, and there is no pull-up on RESETn What changed from the reference design Compared with the reference, I mainly changed: the routing of the differential pairs the placement of the parts the ferrite bead part number mentioned above I can attach the schematic and PCB layout image around the W5500 if needed. My main question is whether the RJ45/magjack layout, CGND handling, or differential pair routing could be causing the link issue, and whether there is anything obvious that I should correct in the PCB layout. Thank you for any advice.

Ethernet Chips

by shiohamu_d 2026-05-02 22:18

Attachments

W5500_pattern.png
W5500_pattern_forword.png
W5500_pattern_back.png
W5500_circuit.png

ESP32
W5500

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